Network traffic is transmitted over a network, such as the Internet, from a sending computer system, via a first network interface card (NIC), to a receiving computer system via a second NIC. The NIC is a piece of hardware found in a typical computer system that includes functionality to send and receive network traffic. Typically, network traffic is transmitted in the form of packets, where each packet includes a header and a payload. The header contains information regarding the source address, destination address, size, transport protocol used to transmit the packet, and various other identification information associated with the packet. The payload contains the actual data to be transmitted from the network to the receiving system.
Each of the packets sent between the sending system and receiving system is typically transmitted through one or more connections. The connections may occur on a physical level. For example, the packets may be transmitted as signals (e.g., electrical, optical, etc) between the two systems through a variety of cables, routers, transmitters, receivers, and/or other interconnected hardware. In addition, the connections may occur on a logical level. For example, in order for the sending system and receiving system to communicate with one another, packets must properly reach the receiving system from the sending system. The receiving device must also recognize that the packets received are indeed meant for the receiving device and separate the packets from other incoming signals. Networking protocols dictate the rules for data representation, signaling, transfer, authentication, and error detection required to transmit information between the sending system and receiving system.
The Open Systems Interconnection Reference Model (OSI model) describes seven different layers that define requirements for communications between two computer systems. The OSI model was developed to enable interoperability between platforms offered by various vendors. Each layer of the OSI model performs services for the layer above and requests services from the layer below. In order from lowest to highest, the layers of the OSI model are: (i) the physical layer, which defines the electrical and physical specifications for devices, (ii) the data link layer, which specifies the transfer of data between network entities, (iii) the network layer, which describes the transmission of variable length data sequences from a source to a destination via one or more networks, (iv) the transport layer, which transfers data between end users, (v) the session layer, which opens, maintains, and closes connections between network devices, (vi) the presentation layer, which transforms data into a form usable by an application, and finally, (vii) the application layer, which allows a user to access the information transmitted over the network.